Core question: is the Expansion Pass worth buying, how do you get into Bubbly Basin, and what do you get that the free 2.0 update does not give you? Short answer: Dive is free for everyone; the town, exclusive Pokémon, and most new items are paid.

Free 2.0 Update vs Paid Pass

Free 2.0Paid Part 1
Dive (taught by Manaphy)Bubbly Basin underwater town
Quality-of-life: bulk storage moves, shared storageExclusive Pokémon (~50-slot Basin dex)
Swim under existing waterBuoyant blocks and floating houses
Watermelon crop, smoothies, ocean furniture
Starmie Dream Island doll, Sharpedo sub room, deep dark trench
Wave breakdown: Part 1 is the town (out now). Part 2 is accessories plus a few extra Pokémon - no new map. Part 3 is another town in 2027.
Redeem your DLC bonuses: open the menu → Downloadable Content and actually hit Receive for the Ditto print recipes. Players missed this and thought recipes never dropped.

Should You Buy Now?

Buy now ifWait if
You finished (or nearly finished) Bleak Beach Environment Level 5, want a big new sandbox, and are fine paying for two later drops you have not seen yet.You are still missing a chunk of the base dex. The DLC does not require a complete base dex, but the loop is the same (habitats → environment level → requests), so unfinished base towns will compete for your attention.

1Unlock Path in Exact Order

Skipping a step is why "content is not yet available" appears or Popplio never shows.

If Popplio is missing: either the paid DLC is not downloaded, or Bleak Beach EL 5 / Dive is not done.

2First Hours in Bubbly Basin

Building decision: use buoyant blocks for mid-water houses, not only the seafloor. Prefab floating houses exist. Do not fully seal a floating house until you have tested interior space - players reported water/air gaps inside enclosed builds.
Farming: Water-specialty Pokémon grow crops underwater, including the new watermelon. Generate-specialty Pokémon power lamps and bubble machines in the dark trench.

3What You Are Collecting

Common Mistakes to Avoid

Priority order: Dive → Popplio → EL 3 habitats → temple + Center → EL 5/10. That loop is what stops the "lost for hours" feeling.